Closed cycle refrigeration systems are well known and are typically used for household refrigeration, commercial refrigeration, freezer units, air conditioning units, heat pumps, and the like. Such systems use a refrigerant which can absorb surrounding heat while passing through an evaporator causing evaporation of the liquid refrigerant to a vapor. After the refrigerant has absorbed heat it is compressed thereby increasing its pressure. The high pressure fluid is passed through a condensing unit, typically located outside the refrigerated space. The heat in the refrigerant is given up to the surrounding, typically to the ambient air or to a liquid coolant. In the condenser, the refrigerant returns to its liquid state. It is then expanded through a throttle, valve or capillary tube to a low pressure fluid and is again sent into the refrigerating mechanism for absorbing heat.
In typical domestic refrigerators, the refrigerant temperatures in the evaporator are approximately 260° K. and the condensing temperature is approximately 300° K., which is slightly above ambient temperature. For freezing operations, the temperature may go a bit lower, and for air conditioning units, the temperature will be a bit higher. It should be understood, that reference to refrigeration in this application generally refers to such systems operating within the above general range of temperatures, including refrigeration, air conditioning and heat pumps, all of which are quite distinct from operating systems at cryogenic temperatures.
From a technical viewpoint, the refrigerant should have appropriate technical characteristics. For example, pressures under which it operates should be within a range of 1-20 atmospheres, and specifically, within the operation range of commercial refrigeration compressors. The high pressure boiling point should be approximately at ambient temperature. The low pressure dew point should be approximately at the freezing point of water. Additionally, in order to be effective, the refrigerant should be non-toxic, non-flammable, and relatively inexpensive.
A wide group of refrigerants have typically been utilized for such refrigeration systems. Many of these are made up of compounds containing one or more of the halogens, including fluorine, chlorine, iodine and bromine. Those containing both chlorine and fluorine are generally referred to as halogenated chlorofluorocarbons, or just chlorofluorocarbons (CFCs). One group of such CFC refrigerants is sold under the brand name Freon® which is a product of the DuPont Company. Various Freon formulations have been utilized, with each of these having differing temperature and pressure characteristics to conform to particular types of refrigeration systems. By way of example, Freon 12, also known as CFC-12 or R-12 (dichlorodifluoromethane) is a popular refrigerant in many refrigerator units. HFC-22, or R-22 is also a common refrigerant, and is chlorodifluoromethane. Additionally, R502 is commonly used, and is a mixture of R-22 (as defined above), and R-115, which is chloropentafluoroethane (C2F5Cl). However, there are questions as to the environmental safety of such CFC's.
Under the Montreal Protocol, as amended, U.S. laws (1990 Clean Air Act), and U.S. Environmental Protection Agency rules, the production and importing of R-12 ended on Dec. 31, 1995. Additionally, only 15% of the baseline amounts of chlorinated fluorocarbons (CFCs) were allowed to be produced or imported into the U.S. during the year 1995 adjusted on an ozone depletion factor basis. R-12 is the major share of that production.
With the effective date of the ban on U.S. R-12 production and importing having passed (Dec. 31, 1995), there has been and is still a need for an efficient replacement for CFC refrigerants with more favorable impact on the environment. Hydrocarbon/CFC blends have been proposed and used, as well as hydrocarbon mixtures.
Hydrocarbon mixtures used to date however, suffer from several drawbacks, minimizing their widespread usage. Propane/propylene mixtures have been used for systems that have excess vapor-handling capacity, can tolerate higher discharge pressures, and would benefit from cooler refrigerant temperatures. Most propane/propylene mixtures in use have greater than 50% propylene, and less than 50% propane.
U.S. Patent Publication No. 2009/0261289 to Ham et al. discloses both CFC/hydrocarbon blends, as well as exclusive hydrocarbon blends. The compositions of the Ham publication however, fail to disclose optimal pressure/temperature relationship, and suitable efficiencies. There remains a need, therefore, for an environmentally favorable hydrocarbon refrigerant with maximum efficiency as drop-in replacement for CFC refrigerants.